1. Field of the Invention
The improvements of this invention pertain to both impulse operated rotary electro-magnetic devices and to stepping motors.
2. Description of the Prior Art
Older prior art in stepping motors has employed some shaping of the rotor and/or stator teeth to establish a preferred direction of rotation when the motor is energized. Other art, particularly as applied to single rotary devices which operate through a limited angle of rotation, has employed rotor or stator tooth tips which vary in radius to reduce the working gap as the rotor and stator teeth come into coincidence to improve the torque characteristics. Varying the radius of both sides of the rotor and stator teeth has been employed in stepping motors to effect a reduction in cogging action but with a loss in sharpness of the detenting action when the motor is used to locate or precisely position an object such as a directly driven printing element.
One recent U.S. Pat. No. 4,264,833 Apr. 1981, Stenudd, employs the technique of tapering both ends or one end of each rotor tooth to achieve certain described advantages, particularly for high stepping frequencies. This tapering or bevelling, however, does not improve the sharpness of the detenting action as does the stepped tooth construction of this invention. Still another recent U.S. Pat. No. 4,341,969 July 1982, Sievert, shows notched teeth for reducing cogging but, like the Stenudd patent structure, is of no help in securing positive sharp detenting.